My 2003 Impala 3.4 liter has been throwing the P0440, Evap leak, code for some time now. I erase it, then it comes back after a couple of days. The car runs fine until it starts to go up a hill/ load is put on it. It then starts to make a banging noise and bogs down until I take my foot off the gas. The car has 276,000+ miles on it with original engine and transmission still going. I replaced the fuel evap solenoid a few years ago and recently cleaned the vapor canister. I have checked for vacuum leaks with no luck. It also has a newer gas cap on it.

 

Purge solenoids and EVAP vent solenoids area other possible cause for the P0440. Also a faulty fuel tank pressure sensor can cause this code. A simple check though would be to look at the fresh air inlet toecap canister and make sure it is clean and free of obstructions. Spiders have been known to create webs and lay eggs in them which can also cause this code. Small EVAP leak will not cause a vehicle to have drive ability problems while under load though. You may have another issue going on there